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  • Author: Hisashi Naito x
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Hideyuki Ishii, Toshio Yanagiya, Hisashi Naito, Shizuo Katamoto and Takeo Maruyama

The objective of this study was to investigate the factors affecting ball velocity at the final instant of the impact phase (t 1) in full instep soccer kicking. Five experienced male university soccer players performed maximal full instep kicks for various foot impact points using a one-step approach. The kicking motions were captured two dimensionally by a high-speed camera at 2,500 fps. The theoretical equation of the ball velocity at t 1 given in the article was derived based on the impact dynamics theory. The validity of the theoretical equation was verified by comparing the theoretical relationship between the impact point and the ball velocity with the experimental one. Using this theoretical equation, the relationship between the impact point and the ball velocity was simulated. The simulation results indicated that the ball velocity is more strongly affected by the foot velocity at the initial instant of the impact phase than by other factors. The simulation results also indicated that decreasing the ankle joint reaction force during ball impact shifts the impact point that produces the greatest ball velocity to the toe side and decreasing the ankle joint torque during ball impact shifts the impact point that produces the greatest ball velocity to the ankle side.

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Shinya Ogaya, Hisashi Naito, Akira Iwata, Yumi Higuchi, Satoshi Fuchioka and Masao Tanaka

Toe-out angle alternation is a potential tactic for decreasing the knee adduction moment during walking. Published reports have not examined the medial knee contact force during the toe-out gait, although it is a factor affecting knee articular cartilage damage. This study investigated the effects of increased toe-out angle on the medial knee contact force, using musculoskeletal simulation analysis. For normal and toe-out gaits in 18 healthy subjects, the muscle tension forces were simulated based on the joint moments and ground reaction forces with optimization process. The medial knee contact force during stance phase was determined using the sum of the muscle force and joint reaction force components. The first and second peaks of the medial knee contact force were compared between the gaits. The toe-out gait showed a significant decrease in the medial knee contact force at the second peak, compared with the normal gait. In contrast, the medial knee contact forces at the first peak were not significantly different between the gaits. These results suggest that the toe-out gait is beneficial for decreasing the second peak of the medial knee contact force.

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Susumu S. Sawada, I-Min Lee, Hisashi Naito, Koji Tsukamoto, Takashi Muto and Steven N. Blair

Background:

Limited data are available on the relationship between muscular and performance fitness (MPF) and the incidence of type 2 diabetes.

Methods:

A cohort of 3792 Japanese men completed a medical examination that included MPF and cardiorespiratory fitness tests. MPF index composite score was calculated using Z-scores from vertical jump, sit-ups, side step, and functional reach tests.

Results:

The mean follow-up period was 187 months (15.6 years). There were 240 patients who developed type 2 diabetes during follow-up. Relative risks and 95% confidence intervals (CI) for incidence of diabetes across baseline quartiles of MPF index composite score were obtained using the Cox proportional hazards model while adjusting for age, BMI, diastolic blood pressure, cigarette smoking, alcohol intake, and family history of diabetes. The relative risks for developing diabetes across quartiles of MPF index composite scores (lowest to highest) were 1.0 (referent), 1.15 (95% CI 0.83−1.60), 1.10 (0.78−1.55), and 0.57 (0.37−0.90) (P for trend = .061). These results were attenuated after adjustment for cardiorespiratory fitness (P for trend = .125).

Conclusions:

This prospective study suggests that MPF is a predictor of type 2 diabetes, although its predictive ability was attenuated after adjusting for cardiorespiratory fitness.

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Yuko Hashimoto, Ko Matsudaira, Susumu S. Sawada, Yuko Gando, Ryoko Kawakami, Chihiro Kinugawa, Takashi Okamoto, Koji Tsukamoto, Motohiko Miyachi, Hisashi Naito and Steven N. Blair

Background: There are several studies on the relationship between low back pain and physical activity. However, the results of these studies vary, and the relationship between them remains unclear. Therefore, we conducted a cross-sectional study to evaluate the association between objectively measured physical activity and low back pain in Japanese men. Methods: The study included 4022 Japanese men [average age: 47 (10) y]. Daily amount of moderate to vigorous physical activity and step counts were measured using an accelerometer. Low back pain, drinking and smoking, and lifestyle-related diseases were surveyed using a self-administered questionnaire. A logistic regression model was used to evaluate the relationship between physical activity and step counts with persistent low back pain after adjusting for confounders. Results: Persistent low back pain was reported in 428 participants. The multivariable-adjusted odds ratios of presenting persistent low back pain across quartiles of amount of moderate to vigorous physical activity were 1.00 (reference); 0.93 (95% confidence interval, 0.70–1.22); 0.97 (95% confidence interval, 0.74–1.28); and 0.67 (95% confidence interval, 0.50–0.90); P for linearity = .012. Conclusion: We found a significant inverse relationship between objectively measured physical activity and persistent low back pain.